Understanding communication between neurons, who is talking to whom, and what language they are speaking, is essential for discovering how brain circuits underlie brain function and dysfunction. Over the past decades, Neuroscience has made exponential progress toward recording and imaging communication between neurons. In addition, geneticists have recently developed the capability to manipulate neurons with light through the expression of light-activated microbial proteins called opsins. Now, neuroscientists can drive neural circuits in order to determine how they give rise to sensation, perception, and cognitive function. In order to take full advantage of optogenetic tools, we are developing holographic methods to deliver patterned light into brain tissue, to enable simultaneous activation of multiple neurons, independently controlling the strength and timing of light targeted to each cell. Here, we propose to: (1) characterize newly developed opsins to determine which are best suited for holographic activation techniques; (2) implement holographic light patterns in three-dimensions; and, (3) distribute and iteratively optimize the 3D holography system in collaboration with Neuroscientists studying circuits in optically and physiologically diverse neura systems. The end goal is to develop a robust system, capable of manipulating neurons in patterns that mimic naturally occurring activity. Insights gained through this collaborative optimization will be used to inform the design of the commercial prototype developed by our industry collaborator Intelligent Imaging Innovations, Inc. (Denver, CO). The system can thus be widely distributed for neural circuit investigation, both in-vitro and in-vivo, to discover how neual communication gives rise to sensation, perception, cognition, and behavior. Such insights will improve our ability to identify effective targets and methods for treating neurological diseases and disorders.